Galvanometer



May 25;, 1937. H. J. HASBROUCK. JR I 3 GALVANOMETE R Filed May 11, 1935mun lull!!! I INVENTOR- H.J. HASBPOUCK J12,

ATTORNEYS.

" Patented May 25, 1937 UNITED 1 STATES PATENT OFFICE GALVANOMETER HApplication May 11, 1935, Serial No. 20,923

10 Claims.

This invention relates to sound recording apparatus and particularly toam element thereof employed for moving a light beam in accordance withthe variations in sound to be recorded.

5 In the recording; of variable area sound tracks, that is, a soundtrack which varies transversely of the film, the usual method of varyingthe width in accordance with sound to be recorded is by an element knownas a galvanometer. In brief this device comprises a pair .of conductorspositioned in a magnetic field and current, corresponding to soundwaves, is passed through the conductors. A mirror attached to theribbons will vibrate in accordance with the movement of'the wires causedby the current passing therethrough. The moving parts of thegalvanometer are; usually encased in oil to dampen their oscillation,while the case is provided with a lens .to permit light to be pro-:Ieeted onto the mirror and reflected therefrom. This lens is at anangle to the light beam to pre- 20 vent light reflected from its surfacefrom being directed to the film. c

The galvanometer of this invention operates on well known principles butis so constructed as to increase its sensitivity to approximately three0 times that of those now known in the art. In a galvanometer, thereaction to be obtained is dependent upon the current in the conductorsand the strength of the field. The field is limited by 0 practicalconsiderations and the conductors must be fine to avoid inertia thuslimiting their current carrying capacity. Other means, therefore, mustbe provided for increasing the reaction of the mirror. such meansforming the subject matter of this invention.

The object of the invention is to obtain greater sensitivity of thegalvanometer and to provide a simple rugged construction which willproduce this sensitivity. I I

o l-Iithertofore it has been the practice in constructing a galvanometerto string the conductors from a fixed point, over a bridge, through amagnetic field, over a second bridge, around a horn at some distancefrom the bridge, and back a over the two bridges to a point adjacent thefirst point. This made a long conductor length which dissipated moreenergy going to and from the magnetic field than was actually used inthe field itself. The present invention is directed,v there- 50 fore, toa construction which reduces this conductor to a length which liessubstantially. wholly within the magnetic field thus permitting all thecurrent the conductors, or ribbons as they are sometimes called, and theentire length of the l ribbonsto function for deflecting the mirrorattached thereto. Also, means are provided for adjusting the tension ofthe ribbons from outside the case of the galvanometer;

The invention will be more fully understood by reference to thefollowing description read in conjunction with the accompanying drawing,in which i Fig. 1 is a sectional elevation view of a preferred form ofgalvanometer and is taken along the line i-l of Fig. 2.

Fig. 2 is a. sectional elevation view taken along line 22 of Fig. 1.

Fig. 3is a sectional plan view taken along line 33 of Fig. 1; and

Fig. 4 is a sectional plan view taken along line 4-4 of' Fig. 1.

As shown in Fig. 1, the equipment ordinarily employed in sound recordersof the variable area type comprises a light source i which sends a beamof light 2 through a light mask or diaphragm 3 one edge of whichprovides the light beam with a cutting edge to define the clear and theexposed portions of the sound track. Suitable lenses 4 and 5 associatedwith the diaphragm 3 project the light beam upon the mirror 6 of agalvanometer I. The mirror 6 is made to vibrate about a vertical axis inaccordance with a modulated current introduced within the galvanometer,as will be explained later.

The light beam 2 which is modulated by vibratingmirror 6 is reflectedthrough a slit disc 8 30 having a slit 9 therein and thence throughobjective lenses ill where it is projected upon the, film H in the formof a narrow strip of light of varying width.

The galvanometer 1 comprises a base l2 of a non-magnetic material suchas brass and has a cover l3 attached thereto as by screws l4 and iii.

The mirror 6 is attached to a pair oi. thin metallic ribbons l6 and i|which are mounted at their lower ends on supports it and It. Thesesupports i8 and I9 are spaced apart from each other slightlyand areinsulated from the base l2 by a piece of insulation such as bakelite 20.Clamping pieces 2| and 22 clamp the ribbons l6 and I1 securely onto thesurfaces of *thesupports l8 and It by screws 23. A thin sheet ofinsulation 60 may be inserted between the supports l8 and 19. to preventaccidental shorting across the ends of the conductors i6 and II. Theupper ends of the ribbons i6 and I! are secured to the end of abell-crank lever 24 by a clamping piece 25 and screws 26. The bell-crank24 is pivoted at 21 (Fig. 1) in trunnion bearings comprising screws 28and 29 (Fig. 2) mounted in blocks 55 38 and 3|, which are.secured to thebase I2 by screws 30' and 3|. The screws 28 and 29 are conical at theirends and engage countersunk portions on either side of the bell-crank24, as shown in Fig. 2. The end 32 f the bell-crank 24 is engaged byspring 33' mounted within a threaded aperturz 34. A screw 35 is providedat the rear of the spring 34 and may be operated by a suitable tool suchas a screwdriver from the exterior of the base I2 to adjust the tensionof the conductors I6 and I! to the proper amount. The interior of thegalvanometer is filled with oil and to prevent it from leaking past thescrew 35 a cap screw 36 is provided having a gasket 31 provided thereon.

The magnetic field of the galvanometer is provided by a pair of softiron pole pieces 38 and 39 mounted adjacent the conductors I6 and I! andare engaged at their outer ends by a U-shaped permanent magnet 40 whichmay be cemented or otherwise suitably secured to the base I2. The polepieces 38 and 39 are undercut at 4I and 42 (Fig. 3) to allow thebell-crank 24 to project therethrough. In order to adjust the polepieces 38 and 39 in respect to the conductors I6 and I1, elongatedcounterbored holes are provided therein in which are mounted screws 44to clamp the pieces 38 and 39 to the base I2. If, after adjustment ofthe pole pieces 38 and 39 a space intervenes between their outer edges.and the inner surfaces of the magnet 40, magnetic shims as 45 and 46 areinterposed therein.

Referring to Fig. 4, a pair of studs 41 and 48 are threadably mountedwithin the conductor supports I8 and I9 and project through holes in theinsulating strip 20 and thence through sleeves 48 and 50 of insulatingmaterial mounted in the base I2. An insulating strip I is provided atthe rear of the base against which nuts 52 and 53 on the studs 41 and 48bear. The outer ends of the studs 41 and 48 serve as terminals whichreceive current from suitable amplifiers in the sound recording circuit.Current passing, for example, through the stud 41, goes through thesupport I8, through conductor I6 to the bellcrank 24 where it returnsthrough conductor I'l, thence through support I9 and on out through thestud 48. v

A lens 54 is placed in a threaded hole 55 provided in the cover I3adjacent the mirror 6. A pair of retainer rings 56 and 51 on either sideof the lens 54 hold it in position and also prevent leakage of oil.Referring to Fig. 4, it will be noted that the lens 54 is mounted at anangle to the plane of the mirror 6. Thus any light which may bereflected from its front and rear surfaces will be directed to one sideof the sound track of the film being recorded. As a further precautionagainst reflected light other than that from the mirror 6 striking thefilm, the conductors I6 and I1 and the sides of the mirrors arepreferably coated with a black paint.

Referring now to Fig. 2, a pair of screws 58 and 59 are provided in thetop of the cover I3. When the galvanometer is to be filled with oil thescrews 58 and 59 are removed and oil is inserted through one of theholes, the other allowing air to escape therethrough. In stringing thegal-- vanometer the ribbons I6 and I! are placed upon the supports I8and I9. A piece of thin metal such as shim stock is placed between theribbons so as to space them apart a required distance which in actualpractice may be about .005 inches. The clamps 2| and 22 are then securedand the piece of shim stock removed. The same procedure is followed insecuring the upper ends of the ribbons I6 and I! to obtain the correctspacing. The mirror 6 is then secured by a suitable cement so that itbridges the two ribbons. After the cover has been attached and thegalvanometer is filled with oil, the tension screw 35 is adjusted untilthe ribbons will vibrate. at a required resonant frequency which in thiscase may be about 8,000 cycles per second.

What is claimed is:

1. In a galvanometer, a casing, a magnet within said casing, pole piecesfor said magnet, a pair of movable conductors having a comparativelyhigh resistance and positioned between said pole pieces and attachedimmediately adjacent both ends of said pole pieces, and means forelectrically connecting one set of the terminals of said conductorsexternally of said casing.

2. In a galvanometer, the combination of an oil-tight casing, a magnetwithin said casing, a pair of pole pieces adjustably mounted between thepoles of said magnet, a pair of movable conductors having acomparatively high resistance and positioned intermediate and attachedimmediately adjacent both ends of said pole pieces, a metallic clamp foradjustably positioning and electrically connecting one set of adjacentterminals of said conductors, insulated clamps for positioning andindividually connecting the other terminals of said conductors, and amirror attached to said conductors substantially midway between saidclamps.

3. A galvanometer in accordance with claim 2 in which said clamp forsaid first mentioned terminals is adjustable from without said casingfor tensioning said conductors.

4. In an instrument for producing mechanical motion corresponding to thevariations in electrical current, the combination of a base, a cover ofinsulating material having therein a lens for admitting light to andfrom the interior of said instrument, said lens being positioned at anangle with respect to light passing to and from the interior of saidinstrument, a permanent magnet having adjustably mounted pole piecesarranged to form a narrow air gap, an L-shaped member pivoted withinsaid instrument. means for mounting one set of terminals of a pair ofmovable conductors having a comparatively high resistance and to one endof said L- shaped member positioned immediately adjacent one end of saidair gap, means for adjusting the position of the other end of saidL-shaped member from without said instrument, means positionedimmediately adjacent the other end of said air gap for attaching theother terminals of said conductors, a reflector on said conductors forreflecting light through said lens in a predetermined direction, andmeans for supplying current to said last mentioned terminals.

5. In a galvanometer the combination of an oil-tight casing, a permanentmagnet within said casing, a pair of pole pieces forming a narrow airgap, and a pair of movable conductors having a comparatively highresistance for carrying current in opposite directions and having asuspension located substantially wholly within said air gap.

6. In a galvanometer the combination of an oil-tight casing, a permanentmagnet, within and attached to the base of said casing, a pair ofadjustable pole pieces between the poles of said magnet and forming anair gap between said pole' pieces, a pair of movable conductors having acomparatively high resistance for carrying ourrent in oppositedirections, means for suspending I said conductors substantially whollywithin the air gap of said pole pieces, a mirror attached to saidconductors, and means for passing light to and from said mirrors.

7. A galvanometer comprising a casing having a. light transmittingopening therein, means with- 'in said casing for producing a steadymagnetic field, a pair of movableconductors having a comparatively highresistance located in said field, each of said conductors carryingcurrent in a direction opposite to the other, a mirror attached to saidconductors, means for impressing current on said conductors, and meansfor mounting said conductors-so that the current in said conductors andthe entire length'of said conductors is effective to move said mirror.

8. A galvanometer in. accordance with claim 7 in which said casing isoil filled and contains means for adjusting said conductors from withoutsaid casing.

9. A galvanometer-comprising an oil filled casing having a lighttransmitting opening therein, means within said casing for producing asteady magnetic field, means for positioning a pair of movableconductors having a comparatively high resistance in said field forcarrying current in opposite directions, a lightrefiector adapted to bemoved by said conductors and means for conducting current to and fromsaid conductors, only that portion of said conductors lying within saidfield carrying said current.

10. A galvanometer in accordance with claim 9 in which said conductorpositioning means is adjustable to vary the tension of said conductorsexternally of said casing.

HAROLD JANSEN HASBROUCK, JR.

